# Finite projective planes, Fermat curves, and Gaussian periods

Journal of the European Mathematical Society (2008)

- Volume: 010, Issue: 1, page 173-190
- ISSN: 1435-9855

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topThas, Koen, and Zagier, Don. "Finite projective planes, Fermat curves, and Gaussian periods." Journal of the European Mathematical Society 010.1 (2008): 173-190. <http://eudml.org/doc/277510>.

@article{Thas2008,

abstract = {One of the oldest and most fundamental problems in the theory of finite projective planes is to classify those having a group which acts transitively on the incident point-line pairs (flags).
The conjecture is that the only ones are the Desarguesian projective planes (over a finite field). In this paper, we show that non-Desarguesian finite flag-transitive projective planes exist if and only if certain Fermat surfaces have no nontrivial rational points, and formulate several other equivalences involving Fermat curves and Gaussian periods. In particular, we show that a non-Desarguesian flag-transitive projective plane of order $n$ exists if and only if $n>8$, the number $p=n^2+n+1$ is prime, and the square of the absolute value of the Gaussian period $\sum _\{a\in \mathcal \{D\}_n\}\zeta ^a$ ($\zeta =$ primitive $p$th root of unity, $\mathcal \{D\}_n=$ group of $n$th powers in $\mathbb \{F\}^\times _p$) belongs to $\mathbb \{Z\}$. We also formulate a conjectural classification of all pairs $(p,n)$ with $p$ prime and $n\mid p-1$ having this latter property, and give an application to the construction of symmetric designs with flag-transitive automorphism groups. Numerical computations are described verifying the first conjecture for $p<4\times 10^\{22\}$ and the second for $p<10^7$.},

author = {Thas, Koen, Zagier, Don},

journal = {Journal of the European Mathematical Society},

keywords = {flag-transitive projective plane; Gauss sum; Jacobi sum; Fermat surface; prime; Flag-transitive projective plane; Gauss sum; Jacobi sum; Fermat surface; prime},

language = {eng},

number = {1},

pages = {173-190},

publisher = {European Mathematical Society Publishing House},

title = {Finite projective planes, Fermat curves, and Gaussian periods},

url = {http://eudml.org/doc/277510},

volume = {010},

year = {2008},

}

TY - JOUR

AU - Thas, Koen

AU - Zagier, Don

TI - Finite projective planes, Fermat curves, and Gaussian periods

JO - Journal of the European Mathematical Society

PY - 2008

PB - European Mathematical Society Publishing House

VL - 010

IS - 1

SP - 173

EP - 190

AB - One of the oldest and most fundamental problems in the theory of finite projective planes is to classify those having a group which acts transitively on the incident point-line pairs (flags).
The conjecture is that the only ones are the Desarguesian projective planes (over a finite field). In this paper, we show that non-Desarguesian finite flag-transitive projective planes exist if and only if certain Fermat surfaces have no nontrivial rational points, and formulate several other equivalences involving Fermat curves and Gaussian periods. In particular, we show that a non-Desarguesian flag-transitive projective plane of order $n$ exists if and only if $n>8$, the number $p=n^2+n+1$ is prime, and the square of the absolute value of the Gaussian period $\sum _{a\in \mathcal {D}_n}\zeta ^a$ ($\zeta =$ primitive $p$th root of unity, $\mathcal {D}_n=$ group of $n$th powers in $\mathbb {F}^\times _p$) belongs to $\mathbb {Z}$. We also formulate a conjectural classification of all pairs $(p,n)$ with $p$ prime and $n\mid p-1$ having this latter property, and give an application to the construction of symmetric designs with flag-transitive automorphism groups. Numerical computations are described verifying the first conjecture for $p<4\times 10^{22}$ and the second for $p<10^7$.

LA - eng

KW - flag-transitive projective plane; Gauss sum; Jacobi sum; Fermat surface; prime; Flag-transitive projective plane; Gauss sum; Jacobi sum; Fermat surface; prime

UR - http://eudml.org/doc/277510

ER -

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